Abstract: A study on the pioidy of Carassius auratus and its geographical distribution in Heilongjiang main river was carried out. Specimens were collected from ten different waters. In studying the karyotype the method of iyrnphocyte euiture and the airdrying teehniqus to prepare examples of cells were used. The result showed that there are two subspecies of Carassius auratus in. Heilongjiang river system. one is Carassius auratus gibelio (Bioch) with 3_n=156. Its Tiaryotype consists of chromosomes about m22 pairs, sm 32 pairs, st and t 24 pairs. Tha sum of Chromosome's arms amounts to 2fi4. The other is C. auratus with 2_n=100, The karyotype consists of chromosomes about m 15 pairs, sm 17 pairs, st and t 18 pairs. The sum of chromosome's arm arxounts to 164. The distribution of ploidy is limited in loc.atian. The diploid fish are distributed in Wuyuer river of the Nenjiang river system and in the marsh lakes surrounding it. The large reservoirs and lakes are the good places for the distribution of triplaid fish, while in all of main rivers and its branchs are tributed the mixture of two types. The origin as well as the classification of Carassius auratus by the view point of cytology combined. with the historical geology are disscussed.